1. Field of the Invention
The invention relates to a read device for a record carrier on which is recorded a data signal representing data words, added codewords of a first type and added codewords of a second type, the added codewords of the first type having a predefined first relation to the data words, and the added codewords of the second type having a second predefined relation to the data words and the added codewords of the first type. The first and second relations determine a preliminary error correction. The data signal is subdivided into blocks which each comprise a control portion containing control data and a data portion containing user-supplied data.
Such a record carrier and device are known, for example, by the name of CD-ROM and CD-ROM player.
2. Description of the Related Art
The user-supplied data on a CD-ROM is recorded in a so-termed main channel. Furthermore, there is a so-termed subcode channel which contains addresses in the form of so-termed absolute time codes. The data in the main channel are subdivided into blocks customarily referred to as sectors. Each sector comprises a so-termed sector header which contains, amongst other things, a sector address which corresponds to the absolute time code in the subcode channel, and a data portion which contains the actual user-supplied data. Prior to the data being recorded on the CD-ROM, these data are subjected to a CIRC process which makes error correction possible. In this process so-termed P-redundancy codewords and so-termed Q-redundancy codewords are added. Also, the data from the sector is distributed over a large portion of each recorded signal. The result of this distribution (also denoted interleaving) is that, when the signal is read out, the data of any particular sector will not be available until the time has elapsed that is necessary for reading the data signal portion over which the data words (and associated P and Q-redundancy codewords) for that sector have been distributed. Contrary to the data in the main channel, the data in the subcode channel is available nearly immediately. Therefore, for a rapid search on a record carrier for a sector having a specific address, the address data in the subcode channel are used. A drawback of recording a subcode channel, however, is that as a result the space available for recording in the main channel is reduced.